FARGDUINO / Fuel Air Ratio Gauge Arduino.

This is just a place holder for my Fargduino project. The project consist of a Fuel / Air ratio gauge for gas engines based on the Arduino. The unit will be able to process the signal for up to two O2 sensors.

It will consist of a Interchangeable display head for single and dual O2 sensors and a control module. The Single O2 sensor head have a circle of 20 Led's and a 4 digit 7 segment display in the middle. The Dual O2 head will have just two 4 digits 7 segment display. The 7 segment display on both heads will display the FAR and Voltage of the O2 sensors and in the single head the LED's will give a visual reference point of the FAR.

The control module will handle either display by just placing or removing a jumper. For those O2 sensor that have a heater core the control module will be able to check for continuity of the heater before applying power to it.

All of it is built on a breadboard at the moment but as I start receiving the PCB's and parts I'll be posting photos of the project. :slight_smile:

sounds like a nice project :slight_smile:

what sensor do you use?



sounds like a nice project

what sensor do you use?


Thanks for the compliment, I saw your project and it is very nice also. I'm planning in having the capability to use Narrow or wideband sensors, the code is written for the wideband and 'm working on the narrowband calculations now. The Circuit uses the analog inputs of the ATMEGA328 buffered with LM358 op amps as voltage followers. This in theory will give me a high impedance input and the option to tap into an existing O2 sensor without putting any load to the car's ECU.

The schematic is a work in progress but here is the link.

I'll be following this closely!

It's something I want to feature in my upcoming car rebuild!!

And much as I'm not a big eco-car fan... the clarity has some nice features.

The futuristic hydrogen-consumption gauge changes color and size to reflect hydrogen consumption as your driving conditions change.

Could be quite cool to have an RGB colour effect to the guage. (can an LCD be RGB backlit I wonder???

Blue (lean) shading through to Red the richer it goes

if you want to measure exhaust O² proportion you will need a wideband o² sensor because the other types can only tell you if it is rich or lean but not by how much, their response is very non-linear

but to read a wideband o² sensor accurately is complicated (less so if you give up some accuracy)

IMHO, the best article on the subject is this page

written by the guys behind the megasquirt, it's not a finished product but the theory of operation is very clearly explained

the guy says it can't be done with a 8-bit mcu and that you need a hybrid mcu/dsp chip like the Motorola 56F8323 but "cheap" off the shelf controller use 8-bit AVR like us so it can be done (the Innovate Motorsport LC-1 uses a 8-bit mcu, can anyone confirm ?)

a good Bosch LSU 4.2 wideband O² sensor costs about 39$ btw

be sure to read

"How the Wide Band Sensor Works"
"Precision Wideband Controller Hardware"

it's a LOT of material and you can probably skip the math part until you are actually writing software

it will probably need a couple read for all of that to sink in but after that you will understand wideband O² sensors
and I think there is a big need to an accurate opensource wideband o² sensor controller

hope this helps (and not discourage you :wink: )

Could be quite cool to have an RGB colour effect to the guage.  (can an LCD be RGB backlit I wonder???

Blue (lean) shading through to Red the richer it goes

I really don't know but I did wanted to use a Tri-color 7 segment display and have the digits change colors for lean or rich condition. The only problem is that I could not find a supplier in the US.

hope this helps (and not discourage you  )

discourage?, Not at all ! shodan:

I appreciate all of the good information you gave me. Like you said it will take me some time to digest all of it.


Well These are the 2 optional display heads for the FARGDUINO. On the left is the dual O2 Sensor head and on the right is the Single.

The reason the single head have yellow LED's is because it was the only thing I had on hand. they will be replaced with red LED's as soon as they come in.

Also the single head is housed inside the top part of a cheap flashlight that I cut the handle off, it only cost me a dollar at the Dollar store. I tried to look for an appropriate 51 to 52 mm diameter housing but they are too expensive

At this point I'm still working on the sketch and the control board, I'm looking for a way to calibrate the FARGDUINO to the O2 sensor maximum voltage output on a LEAN condition for the wide band sensor.

Need to do this because after adding the op-amps and extra circuits to the ADC inputs of the ATMEGA the readings from the ADC are offset compared to a direct input to the ADC and when you are dealing with Milli-volts it is important to be as accurate as possible.

This being my first Arduino project I think that I'm doing pretty good. :wink:


using a flashlight housing as a gauge, that is an awesome idea I love it !!!